This invention relates to a method for solidifying liquid radioactive wastes for long-term storage as a solid. The invention further relates to solidifying the liquid waste by calcining in a fluidized-bed calciner. The invention is specifically directed towards the fluidized-bed calcination of liquid radioactive waste containing significant quantities of sodium or sodium compounds.
In the chemical reprocessing of spent nuclear reactor fuel elements to recover the unburned nuclear reactor fuel material, very large volumes of aqueous solutions containing radioactive wastes are generated. In addition to the large volumes produced, these aqueous waste solutions are extremely corrosive and present difficult problems in their handling and storage. Since it is necessary to store these radioactive wastes for extremely long periods of time to permit decay of the highly radioactive fission products included in the wastes, the aqueous wastes are converted to a solid form which, in addition to occupying less volume than the corresponding liquid wastes, is less corrosive and imposes less difficult problems in handling and long-term storage. These aqueous radioactive waste solutions are converted to a solid form by calcining in a fluidized bed in the Waste Calcining Facility at the Idaho Chemical Processing Plant located at the United States Atomic Energy Commission's National Reactor Testing Station in southeastern Idaho. The aqueous solutions are converted to solid form by calcining in a fluidized bed, the aqueous solutions being injected into the fluidized bed through spray nozzles mounted in the walls.
A particular problem is posed in the fluidized-bed calcination of liquid radioactive wastes which contain significant quantities of sodium or sodium compounds. Since a considerable concentration of nitrates will necessarily be present due to the use of acids including nitric acid to dissolve the spent nuclear reactor fuel elements, sodium nitrate can be formed. Sodium nitrate will melt and exist in a molten state between 305.degree.C. and 833.degree.C. Therefore, at the normal calcination temperatures ( 400.degree.-500.degree.C.), sodium nitrate could result in agglomeration of the bed particles and consequent fouling of the fluidized bed. Since agglomeration of the fluidized-bed particles is intolerable, it is desirable to eliminate or minimize the presence of molten sodium nitrate during calcination.
It is an object of the present invention to provide a method for the fluidized-bed calcination of sodium-containing liquid radioactive wastes which will not result in agglomeration of the fluidized-bed particles.
It is a further object of the present invention to provide a method for preventing agglomeration of the fluidized bed by retarding and minimizing the formation of sodium nitrate.